Revisiting the ground state of CoAl${}_2$O${}_4$: comparison to the conventional antiferromagnet MnAl${}_2$O${}_4$

Abstract

The A-site spinel material, CoAl2O4, is a physical realization of the frustrated diamond-lattice antiferromagnet, a model in which is predicted to contain unique incommensurate or `spin-spiral liquid' ground states. Our previous single-crystal neutron scattering study instead classified it as a `kinetically-inhibited' antiferromagnet, where the long ranged correlations of a collinear Neel ground state are blocked by the freezing of domain wall motion below a first-order phase transition at T* = 6.5 K. The current paper expands on our original results in several important ways. New elastic and inelastic neutron measurements are presented that show our initial conclusions are affected by neither the sample measured nor the instrument resolution, while measurements to temperatures as low as T = 250 mK limit the possible role being played by low-lying thermal excitations. Polarized diffuse neutron measurements confirm reports of short-range antiferromagnetic correlations and diffuse streaks of scattering, but major diffuse features are explained as signatures of overlapping critical correlations between neighboring Brillouin zones. Finally, and critically, this paper presents detailed elastic and inelastic measurements of magnetic correlations in a single-crystal of MnAl2O4, which acts as an unfrustrated analogue to CoAl2O4. The unfrustrated material is shown to have a classical continuous phase transition to Neel order at T_N = 39 K, with collective spinwave excitations and Lorentzian-like critical correlations which diverge at the transition. Direct comparison between the two compounds indicates that CoAl2O4 is unique, not in the nature of high-temperature diffuse correlations, but rather in the nature of the frozen state below T*. The higher level of cation inversion in the MnAl2O4 sample indicates that this novel behavior is primarily an effect of greater next-nearest-neighbor exchange.

13 pages, 8 figures, acccepted for publication in Physical Review B

References in corpus (6)

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• A Spin-Orbital Singlet and Quantum Critical Point on the Diamond Lattice: FeSc2S4
• Quantum order by disorder in frustrated diamond lattice antiferromagnets
• Approaching the Ground State of Frustrated A-site Spinels: A Combined Magnetization and Polarized Neutron Scattering Study
• Stripeless incommensurate magnetism in a doped strongly correlated oxide
• Nonconventional magnetic order in frustrated diamond lattice antiferromagnet CoAl2O4 studied by neutron diffraction and classical Monte-Carlo simulation

Cited by in corpus (10)

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• Spin order and dynamics in the diamond-lattice Heisenberg antiferromagnets CuRh2O4 and CoRh2O4
• Cluster glass transition and relaxation in random spinel CoGa2O4
• A molecular diamond lattice antiferromagnet as a Dirac semimetal candidate
• Line-Graph Approach to Spiral Spin Liquids
• Electronic structure of the frustrated diamond lattice magnet NiRh${}_2$O${}_4$
• Disorder effects in spiral spin liquids: Long-range spin textures, Friedel-like oscillations, and spiral spin glasses
• On the complexity of spinels: Magnetic, electronic, and polar ground states
• Codimension-Two Spiral Spin-Liquid in the Effective Honeycomb-Lattice Compound Cs${}_3$Fe${}_2$Cl${}_9$